A transmitter-receiver that handles high-frequency signals uses a waveguide to transmit the signals with high electrical power. However, the signals transmitted through the waveguide cannot be directly handled in an electronic circuit. For this reason, the high-frequency transmitter-receiver uses a waveguide coaxial conversion device that performs conversion of signals between a waveguide transmission system and a coaxial transmission system. Examples of such a waveguide coaxial conversion device are disclosed in Patent Literature 1 and 2.
Patent Literature 1 discloses a waveguide coaxial conversion device having a function of converting a coaxial transmission system to/from a waveguide transmission system, and a function of transmitting/receiving fundamental TE modes with opposite phases to/from a first fundamental TE mode transmission line and a second fundamental TE mode transmission line, respectively, which are partitioned by a metal plate.
Patent Literature 2 discloses a dielectric rod antenna including: a waveguide; a dielectric rod projecting from an opening at a distal end of the waveguide; and a feeding portion provided at a proximal end of the waveguide. In this dielectric rod antenna, a dielectric substrate constituting a fin line F with the width of the electrode thereof gradually decreasing toward the distal end opening is inserted into the waveguide. Accordingly, in Patent Literature 2, the operating frequency band in the fundamental mode is increased by decreasing the cut-off frequency in the fundamental mode, without changing the cut-off frequency of a higher-order mode.